Medical injection devices

ABSTRACT

A firing device has a housing ( 10, 20 ) for an injector ( 1 ) with a trigger ( 4 ) whose action to eject a dose from its needle ( 2 ) is forwards against a resistance. The housing contains a spring ( 24 ) which acts on an axially movable locator ( 23 ) for the injector ( 1 ) that co-operates with its trigger ( 4 ). The device is primed by compressing the spring ( 24 ), the injector then being latched in a rearward position. Release of the catch ( 28 ) causes the spring ( 24 ) first to propel the injector ( 1 ) forwards, acting through the locator ( 23 ) and trigger ( 4 ), until the needle ( 2 ) is projected, and then to overcome the resistance to the trigger ( 4 ) to actuate that and cause a dose to be ejected.

This invention relates to medical injection devices. It is particularlyconcerned with the automatic firing of an injector having a barrel-likebody with a sliding trigger on one side to eject the dose from a needleat its forward end. The action of the trigger is forwards against astiff spring. Preferably, there is a dose setting mechanism such as arotary knob at its rear end which may be “clicked” round to a desiredsetting. All the trigger does is to release a spring which shoots aplunger forwards by an amount determined by the knob, this plungerco-operating with a piston in a capsule carrying the dose.

Such injectors are well known, but they require the user to insert theneedle into the flesh first, before releasing the trigger. Forself-users, this can be particularly difficult: it is natural to flinchand not push the needle in far enough.

The aim of this invention is to provide a device that can automate thisoperation, ensuring that the injector needle is thrust in to the correctdegree before the dose is ejected.

According to the present invention there is provided a a firing devicefor an injector having a barrel-like body with a sliding trigger on oneside to eject the dose from a needle at its forward end, the action ofthe trigger being forwards against a resistance, the device comprising agenerally cylindrical housing for the injector, a forward portion of thehousing, open at its forward end for projection of the injector needle,containing spring means for exerting a light rearward force on theinjector, and a rearward portion of the housing having an axiallymovable, forward spring-loaded member to cooperate with the injectortrigger, an external cocking mechanism operable to energise the springloading of said member, and an operating element to release that loadingto cause the member first, acting through the injector trigger, to shootthe injector forward against the light rearward force of said springmeans to a needle projecting position, and then to overcome saidresistance operate the trigger to eject the dose from the injector.

The spring-loaded member may be generally tubular to embrace theinjector, a coil spring acting between its rear end and an internalabutment at the rear end of the barrel.

Conveniently, an axial slot, open from the forward end of the tubularmember, receives the trigger and thereby locates the injectorrotationally. The trigger will be engaged by the closed rear end of thisslot.

The cocking mechanism is preferably a sleeve over the rearward portionof the housing with at least one lateral projection from the tubularmember projecting through an axially parallel slot in the housing intoan axially parallel slot in the sleeve, the cocking action being to pullthe sleeve rearwardly so that the projection engaged by the forward endof its slot takes the tubular member with it until there is snapengagement between the tubular member and the barrel, the injector beingpushed back at the same time by the spring means.

This arrangement also ensure that there is no mutual rotation betweenthe tubular member, the housing and the sleeve.

Conveniently, the sleeve carries the operating element which can onlyregister in a position to release the snap engagement when the sleeve ismoved forwards again after the device has been cocked. The operatingelement is preferably a button which engages in a slot in the housingand which has two different positions between which it can be shiftedcircumferentially of the sleeve only when that is forwards. In one saidposition it acts by co-operation with a step in the slot as a preventeragainst the sleeve being slid rearwardly, that position also being theone, when the sleeve is moved forwards after cocking, in which thedevice can be fired. In the other said position, it allows the externalsleeve to be slid rearwardly (and forwardly again) but is ineffective,when pressed, to fire the device.

When the device is for an injector having a rear end rotary adjustingknob to set the amount of dose to be ejected, the sleeve, in its forwardposition with the device cocked, conveniently leaves this knob exposedwhereby, before firing, the user can rotate the knob to the requireddosage. Marks on the knob may register with a mark on the end of thesleeve to assist gauging the amount of dosage set.

For a better understanding of the invention one embodiment will now bedescribed, by way of example, with reference to the accompanyingdrawings, in which:

FIG. 1 is a side view of a firing device for an injector with a firingbutton in a locked and firing position,

FIG. 2 is a similar side view but with the firing button in a cockedposition,

FIG. 3 is an axial section of the device, charged with an injector, inan idle position,

FIG. 4 is a similar axial section with the device just cocked,

FIG. 5 is a similar axial section with the device cocked and ready tofire,

FIG. 6 is a perspective view of a locator tube forming part of thedevice,

FIG. 7 is a perspective view of a barrel into which the locator tubefits, and

FIG. 8 is a perspective view of a sleeve into which the barrel fits.

The injector 1 to be fired is of known type and will not be described indetail. But its salient features for the purposes of this specificationare a needle 2 at its forward end, a rotatable knob 3 at its rear endwhich is “clicked” round to set the desired dosage, and an elongatetrigger 4 on the side of the barrel-like body towards the rear end whosefiring action is forwards against a stiff spring or some otherresistance. The body of the injector narrows at a sloping shoulder 5towards a forward end portion which has opposed windows 6 through whichthe capsule containing the medium to be injected can be seen.

The firing mechanism into which this injector fits has two assemblies 7and 8 which screw together at 9. The nose assembly 7 consists of astepped tube 10 with a cylindrical portion 11 forward of a shoulder 12provided with opposed windows 13 which will register with the windows 6.Internally at the shoulder 12 there is an annular rib 14 which limitsthe fore and aft travel of a locator ring 15. This has an outwardlyprojecting rib 16 at its rear end, and a spring 17 acts between that riband the root of the rib 14 to urge the locator ring 15 rearwardly with afairly light force. Two diametrically opposed arms 18 project forwardlyfrom the ring 15 and hooks 19 at their ends can snap past the rib 14 onassembly. The travel of the locator ring is determined by the length ofthese arms 18 to the hooks 19. The locator ring 15 has guide means (notshown) to keep it from rotating while allowing axial movement, and thegaps between the arms 18 register with the windows 13.

The rear assembly 8 consists of a barrel 20, with a wide externalannular rib 21 just to the rear of the screw thread joint 9, a sleeve 22encasing the barrel 20 to the rear of the rib 21, a generally tubularlocator 23 for the injector within the barrel urged forwardly by apowerful spring 24 reacting against an inturned flange 25 at the rearend of the barrel, and a trigger 26 captive to the sleeve 22. The tube10 and barrel 20, screwed together, form a housing.

The locator 23 (FIG. 6) has a wide slot 27 extending lengthways, open atits forward end and with a blind rear end, to accommodate the injectortrigger 4. Diametrically opposite this a tongue 28 is integrally formedwith the tube at its forward end, the free end of the tongue beingthickened to project proud of the otherwise cylindrical envelope. Thebarrel 20 (FIG. 7) has a slot 29 and an aperture 30 with which thistongue 28 can engage. The slot 29 is L-shaped in profile, open to therear end of the barrel and with its short leg forward and alignedaxially with the aperture 30. When the tongue 28 is latched into theslot 29, engaging its forward end, it holds the locator 23 back againstthe compressed spring 24, and when released from that it snaps into theaperture 30 to assist termination of the forward motion of the locator23.

The locator 23 also has two diametrically opposed fins 31 which projectthrough longitudinal slots 32 in the barrel 20, the leading edges ofthese fins being radial but the rear edges having a shallow slope sothat the tube is radially contracted by a wedging action as it is forcedrearwardly into the barrel on assembly. The slot 27 makes thisdeformation possible. When the fins 31 reach the slots 32 they springoutwards making the locator 23 captive to the barrel 20. Furthermore,their tips are then proud of the barrel and the sleeve 22 (FIG. 8) haslongitudinal slots 33 in which those tips can engage in like manner,making the sleeve captive also. The leading ends of the slots 33 serveas stops in a manner described below. The fins 31 also ensure that thereis no mutual rotation between the locator 23, the barrel 20 and thesleeve 22.

A single fin might suffice, but two are preferred.

The trigger 26 has an exposed button 34 projecting through the slot 29,in which it is captive, and through an aperture 35 in the sleeve 22.This aperture allows the button to be shifted circumferentially betweenthe positions shown in FIGS. 1 and 2 when it registers with the wide,forward end of the slot 29. The trigger is retained by a plate-likeextension 36 from its base which engages under the periphery of theaperture 35 and which at its rear end has an inwardly projectingwedge-shaped stud 37. Below the front of the button there is a thickenedportion 38 to co-operate with the tongue 28.

The rear ends of the barrel 20, the sleeve 22 and the locator 23 areopen so that the injector 1 can be fitted as shown in FIG. 3, the rearend of its trigger 4 bearing against the closed end of the slot 27 andits dose adjusting knob 3 just exposed at the rear end of the injector.The sleeve 22 will have a mark against which rotation of the knob 3 canbe gauged; the mark on the injector itself being hidden inside theassembly 8. With the injector so in place, the nose assembly 7 isscrewed on, the locator ring engaging the sloping shoulder 5 of theinjector and being forced forwardly in relation to the tube 10 againstthe spring 17. When assembly is complete, the forward end of the ring 15bears against the rib 14 with the spring 17 compressed. But that springis not nearly powerful enough to overcome the spring 24 and the locator23 remains in the forward position with the tongue 28 in the aperture30.

The needle 2 is left exposed projecting forward of the nose assembly 7.In practice, it will have a protective sheath while this fittingtogether is carried out, and it will not be removed until just beforeuse.

In the FIGS. 1 and 3 position of the trigger 26 the stud 37 is captivein the slot 29, preventing the sleeve 22 from moving rearwardly. Thedevice is in an idle or non-ready condition.

For use, the trigger 26 is pushed circumferentially to the FIG. 2position to take the stud 37 out of engagement with the step formed bythe short leg of the L-shaped slot 29. This trigger movement also takesthe thickened portion 38 out of axial alignment with the tongue 28. Thesleeve 22 can then be pulled back and, acting through the forward endsof its slots 33 and the fins 31, this also retracts the locator 23,compressing the spring 24. When fully retracted, the tongue 28 snapsinto the slot 29, latching the device in the position of FIG. 4. Duringthis operation the injector 1 is pushed back by the spring 17 actingthrough the locator ring 15 and the needle 2 is withdrawn into the tube10.

The sleeve 22 is now slid forwards again to abut the rib 21, fullyexposing the knob 3, which is rotated to set the required dose. Thetrigger 26 is pushed back circumferentially to the FIG. 1 position sothat the stud 37 re-enters the short leg of the slot 29 while theportion 38 comes directly over the free end of the tongue 28. In thisposition of FIG. 5 the device is ready to fire.

The free end of nose portion 11 is held against the area of skin wherethe injection is to be made and the button 34 pressed. This releases thetongue 28 from the slot 29 and the spring 24 shoots the locator 23forwards. The closed end of the slot 27 bearing on the trigger 4 carriesthe injector forwards as well, causing the needle 2 to penetrate theskin. The trigger 4 is not immediately activated, being held rearwardlyby a spring or other resistance stiffer than the spring 17. But when thelocator ring 15 meets the rib 12, the trigger 4 will be pressed forwardsufficiently to trip the action of the injector. The dose is thereforeejected as the forward travel of the injector is completed, back to theFIG. 3 condition. The knob 3 returns to its zero position during thisejection.

The cycle is then ready to be repeated.

1. A firing device for use with an injector of the type having abarrel-like body enclosing a spring-loaded plunger to act on a pistonwithin a capsule carrying a dose, and a sliding trigger on one side ofthe body actuable to release the plunger spring to drive the plunger tocause ejection of the dose from a needle at the forward end of the body,the action of the trigger being forwards against a resistance, thefiring device comprising a generally cylindrical housing surrounding theinjector, a forward portion of the housing, open at its forward end forprojection of the injector needle, containing a locator spring forexerting a light rearward force on the injector to cause the needle tobe located within said housing, and a rearward portion of the housinghaving an axially movable, forward spring-loaded actuating member tocooperate with the injector trigger, an external cocking mechanismoperable to energize the spring loading of said actuating member with aspring force greater than said light rearward force, and an operatingelement to release that loading to cause the actuating member firstly,acting through the injector trigger, to shoot the injector forwardagainst the light rearward force of said locator spring to a needleprojecting position, and secondly to overcome said resistance in theinjector and operate the injector trigger to cause ejection of the dosefrom the injector, said generally cylindrical housing being in two partsseparably secured together in end-to-end relationship thereby releasablyto contain a said injector, and wherein the spring-loaded member isgenerally tubular to embrace the injector, a coil spring acting betweenits rear end and an internal abutment at the rear end of the housing andwherein the cocking mechanism is a sleeve over the rearward portion ofthe housing with at least one lateral projection from the tubular memberprojecting through an axially parallel slot in the housing into anaxially parallel slot in the sleeve, the cocking action being to pullthe sleeve rearwardly so that the projection engaged by the forward endof its slot takes the tubular member with it until there is snapengagement between the tubular member and the barrel, the injector beingpushed back at the same time by said spring means.
 2. A firing device asclaimed in claim 1, wherein an axial slot, open from the forward end ofthe tubular member, receives the trigger and thereby locates theinjector rotationally.
 3. A firing device for use with an injector ofthe type having a barrel-like body enclosing a spring-loaded plunger toact on a piston within a capsule carrying a dose, and a sliding triggeron one side of the body actuable to release the plunger spring to drivethe plunger to cause ejection of the dose from a needle at the forwardend of the body, the action of the trigger being forwards against aresistance, the firing device comprising a generally cylindrical housingsurrounding the injector, a forward portion of the housing, open at itsforward end for projection of the injector needle, containing a locatorspring for exerting a light rearward force on the injector to cause theneedle to be located within said housing, and a rearward portion of thehousing having an axially movable, forward spring-loaded actuatingmember to cooperate with the injector trigger, an external cockingmechanism operable to energize the spring loading of said actuatingmember with a spring force greater than said light rearward force, andan operating element to release that loading to cause the actuatingmember firstly, acting through the injector trigger, to shoot theinjector forward against the light rearward force of said locator springto a needle projecting position, and secondly to overcome saidresistance in the injector and operate the injector trigger to causeejection of the dose from the injector, wherein the spring-loaded memberis generally tubular to embrace the injector, a coil spring actingbetween its rear end and an internal abutment at the rear end of thehousing, and the cocking mechanism is a sleeve over the rearward portionof the housing with at least one lateral projection from the tubularmember projecting through an axially parallel slot in the housing intoan axially parallel slot in the sleeve, the cocking action being to pullthe sleeve rearwardly so that the projection engaged by the forward endof its slot takes the tubular member with it until there is snapengagement between the tubular member and the barrel, the injector beingpushed back at the same time by said spring means.
 4. A firing device asclaimed in claim 3, wherein the sleeve carries the operating elementwhich can only register in a position to release the snap engagementwhen the sleeve is moved forwards again after the device has beencocked.
 5. A firing device as claimed in claim 4, wherein the operatingelement is a button which engages in a slot in the housing and which hastwo different positions between which it can be shiftedcircumferentially of the sleeve only when that is forwards, wherein inone said position it acts by co-operation with a step in the slot as apreventer against the sleeve being slid rearwardly, that position alsobeing the one, when the sleeve is moved forwards after cocking, in whichthe device can be fired, and wherein in the other said position, itallows the external sleeve to be slid rearwardly (and forwardly again),but is ineffective, when pressed, to fire the device.
 6. A firing deviceas claimed in claim 3, wherein the device is for an injector having arear end rotary adjusting knob to set the amount of dose to be ejected,and wherein the sleeve, in its forward position with the device cocked,leaves this knob exposed whereby, before firing, the user can rotate theknob to the required dosage.
 7. A firing device as claimed in claim 6,wherein marks on the knob register with a mark on the end of the sleeveto assist gauging the amount of dosage set.